Without doing immoral against immoral, you can't win.

[river_flow]

IMO
You must treat people who has treated you right/ whom you meet first/ against whom you have no evidence of immorality in a moral manner.

But you must be immoral against a immoral person or one who has treated you in immoral manner previously . Otherwise you can't win in life.
Only a iron can cut a iron.

 

[fastnbulbous]

We must fight fire with fire.

 

[coursehawk69]

You're describing classic Tit for Tat strategy. There are computer simulations that reveal it to be a dominant strategy in some games where players compete for limited resources.